I am looking for some suggestions/advice/tips - anything as I have been asked to do a shoot in a lovely location but I'm a little perplexed as how to best "light" the model...

Here is a shot I took several years ago of the location:

It's a waterfall about an hour & 1/2 north of Pittsburgh in a state park. The model that I'll be shooting wants some bikini shots with her at the base of the falls. That alone presents some challenges like: water temperature, depth of the water, flow over the falls, time of day/amt of light - etc but I am familiar with the area and these falls so I believe I'll be able to handle those issues...

What I'm looking for here is suggestions on how to best light the model AND capture some movement of the falls... I've never attempted to do a shoot like this where I'm hoping to capture some movement of the falling water with a slow shutter speed while at the same time capturing a person in the frame without overexposing... I'm thinking I may need to experiment prior to doing the shoot with some neutral density filters, maybe rear curtain flash... etc?

And that's what I'm looking for... Has anyone here ever done a similar shoot capturing both a model in this type of setting with a slow shutter speed?

I'm thinking one light source to keep things simple, maybe a B800 through a diffused 22" beauty dish with a boom (held by an assistant) or thru a large umbrella. Triggered w/cybersyncs, powered with a vagabond. Camera on a tripod of course...